1. Field of the Invention
The present invention relates to a multi-laser scanning unit (LSU) capable of diffracting and scanning light incident from at least two light sources, and more particularly, to a multi-LSU in which a plurality of scanning lines (rays) incident parallel onto a photoreceptor are also directionally the same.
2. Description of the Related Art
In general, a multi-LSU is adopted in a color printer and is used to form a plurality of latent electrostatic images required to develop a color image in combination with a plurality of colors including yellow (Y), magenta (M), cyan (C), black (K) and the like. In this case, a plurality of scanning lines scanned by the multi-LSU and incident onto a photoreceptor such as a photosensitive belt or photosensitive drum, must be parallel at predetermined intervals, such that scanning directions of the plurality of scanning lines are parallel to each other.
Referring to FIGS. 1 through 3, a conventional multi-LSU capable of generating four scanning lines corresponding to the colors Y, M, C and K, includes a driving source 11 for providing a rotatory force, a deflection disk 15 having a plurality of sectors each with a hologram pattern 15a, and a light source unit 20 which is arranged facing one surface of the deflection disk 15 and which radiates light onto the deflection disk 15. The light source unit 20 includes four light sources 21, 23, 25 and 27, which irradiate light onto four incident points S.sub.1, S.sub.2, S.sub.3 and S.sub.4, respectively, wherein each pair of points adjacent to each other form a right angle at the rotary center of the deflection disk 15. Also, the four incident points Si, S.sub.2, S.sub.3 and S.sub.4, are positioned with equal radii from the rotary center of the deflection disk 15. Thus, the centers of the scanning lines formed by the deflection disk 15 pass the center of the deflection disk 15, thereby reducing the off-axis.
The incident light lines are diffracted by the hologram patterns 15a by rotation of the deflection disk 15 and form scanning lines L.sub.11, L.sub.21, L.sub.31 and L.sub.41 in the directions indicated by the arrow (.fwdarw.). Here, the scanning lines L.sub.11 and L.sub.31 are parallel (to the Y-axis) and are opposite in direction. Also, the scanning lines L.sub.21 and L.sub.41, perpendicular to the scanning lines L.sub.11 and L.sub.31, are parallel (to the X-axis) and are opposite in direction.
Traveling paths of the scanning lines L.sub.11, L.sub.21, L.sub.31 and L.sub.41, are changed by a plurality of mirrors such that the centers of the scanning lines travel along the X-axis. That is, the scanning line L.sub.11 is reflected by a mirror M.sub.1 to travel in the X-axis direction, and the scanning line L.sub.21 is reflected by a mirror M.sub.21 toward the rotary center of the deflection disk 15 and then reflected again by a mirror M.sub.22 positioned on the rotary center of the deflection disk 15 to travel in the X-axis direction. Also, the scanning line L.sub.31 is reflected by a mirror M.sub.3 to travel in the X-axis direction, and the scanning line L.sub.41 is reflected by a mirror M.sub.41 toward the rotary center of the deflection disk 15 and is reflected again by a mirror M.sub.42 positioned on the rotary center of the deflection disk 15 to travel in the X-axis direction.
Scanning directions of scanning lines L.sub.12, L.sub.22, L.sub.32 and L.sub.42, scanning in the X-axis direction after being reflected by the mirrors M.sub.1, M.sub.21, M.sub.22, M.sub.3, M.sub.41 and M.sub.42, are indicated by the arrow (.fwdarw.) in FIG. 2. As shown in FIG. 2, the scanning lines L.sub.12, L.sub.22 and L.sub.42 have the same scanning directions, but the direction of the scanning line L.sub.32 is opposite to that of the scanning lines L.sub.12, L.sub.22 and L.sub.42.
That is, in the case of using a plurality of mirrors and post-holographic optical elements to change the traveling path of the light, after being reflected by the mirrors M.sub.1, M.sub.22, M.sub.3 and M.sub.42, the plurality of scanning lines are parallel in scanning directions for a photoreceptor, but the direction of the scanning line L.sub.32 is still opposite to that of the others.
Thus, when forming an image on the photoreceptor, image information must be compensated for in the circuitry due to the different scanning directions. That is, the light source 25 providing the scanning line L.sub.32 must transfer the image data in the opposite direction to match image provided by the remaining light sources 21, 23 and 27. That is, there is a disadvantage in that the light sources 21, 23 and 27 provide image information in the direction indicated by .times. while the light source 25 provides image information in the direction indicated by .circle-w/dot. as shown in FIG. 3, so that image data processing is complicated.